1. Field of the Invention
The present invention relates to an absorbent article to be worn on the human body to absorb liquid and more particularly to an absorbent article suitable for use as a sanitary napkin.
2. Description of the Related Art
Absorbent articles such as sanitary napkins are typically constructed to include a liquid absorbent layer which contains fluff pulp and whose skin-side surface is covered with a liquid passage layer (topsheet). This liquid passage layer allows rapid transfer of an applied liquid into the liquid absorbent layer and is preferably constructed to prevent a liquid applied to the liquid absorbent layer from returning to the skin-side surface of the absorbent article.
Japanese Unexamined Patent Publication No. H04-24263 discloses a liquid passage layer which is constructed by stacking two nonwoven fabrics. Since the liquid passage layer is constructed of nonwoven fabrics having a lot of voids therein, a liquid applied to the skin-side surface of the absorbent article is allowed to easily reach the liquid absorbent layer through the voids. The nonwoven fabric is also intended to provide an improved feeling when in contact with the human bodies.
Japanese Unexamined Patent Publication No. H09-507408 discloses a liquid passage layer which is constructed of a resin film having a large number of liquid passage apertures and a nonwoven fabric disposed beneath the resin film. In the liquid passage layer, a liquid applied to the skin-side surface of the resin film passes through the liquid passage apertures of the resin film and then passes through the nonwoven fabric for absorption into the liquid absorbent layer. The nonwoven fabric, which is disposed between the resin film and the liquid absorbent layer to put distance therebetween, effectively prevents a liquid absorbed in the liquid absorbent layer from returning to the skin-side surface of the resin film. In addition, from whitening the resin film, it is also expected that the color of liquid absorbed in the liquid absorbent layer will be less noticeable in surface view of the absorbent article.
Japanese Unexamined Patent Publication No. H11-513904 discloses a liquid passage layer which is constructed by stacking two resin films. The two resin films are individually formed with a large number of liquid passage apertures, but the liquid passage apertures in the upper resin film (the resin film located on the skin-side surface of the liquid passage layer) have a larger individual open area than the liquid passage apertures in the lower resin film (the resin film located on the garment-side surface of the liquid passage layer) and the upper resin film has a larger percent open area due to the liquid passage apertures than the lower resin film. The upper resin film, which is less resistant to liquid passage, allows rapid passage of an applied liquid, while the lower resin film allows gradual passage of a liquid introduced into the space between the upper resin film and the lower resin film for absorption into the liquid absorbent layer. In the liquid passage layer, the resistance to liquid passage is higher in a direction from the liquid absorbent layer to the skin-side surface of the liquid passage layer than in a direction from the skin-side surface of the liquid passage layer to the liquid absorbent layer, so that a liquid absorbed in the liquid absorbent layer is less apt to return to the skin-side surface of the liquid passage layer.
In the case where the liquid passage layer is constructed by stacking two nonwoven fabrics, as described in Patent Publication No. H04-24263, resistance to liquid passage in the direction from the skin-side surface of the liquid passage layer to the liquid absorbent layer is almost equal to that in the direction from the liquid absorbent layer to the skin-side surface of the liquid passage layer. Therefore, when body pressure is exerted on the skin-side surface of the liquid passage layer, a liquid absorbed in the liquid absorbent layer easily passes through the nonwoven fabrics to return to the skin-side surface of the liquid passage layer. In addition, while the nonwoven fabrics are permeable to liquid, liquid is apt to be retained inside them and remain behind. Inside the nonwoven fabrics, more specifically, voids of various sizes are defined between fibers. While a liquid given to large voids easily passes through them under gravitation to migrate toward the liquid absorbent layer, a liquid introduced into small voids is finely divided to have a small weight, so that it tends to be retained in the small voids without migrating toward the liquid absorbent layer. In the case where the liquid passage layer consists essentially of nonwoven fabrics, because liquid is apt to return to the skin-side surface of the liquid passage layer from the liquid absorbent layer and is also apt to remain inside the liquid passage layer, as set forth above, the wearer's skin tends to be wetted to cause discomfort.
The liquid passage layer disclosed in Patent Publication No. H09-507408 is more effective in preventing wetting of the skin-side surface of the liquid passage layer than that disclosed in Patent Publication No. H04-24263, because a resin film having a large number of liquid passage apertures is laid on a nonwoven fabric. However, the nonwoven fabric located beneath the resin film is apt to retain liquid and cannot easily recover to its original state from a compressed state because when body pressure is exerted on the nonwoven fabric in a liquid retaining state, its elasticity decreases. Therefore, the distance between the liquid absorbent layer and the resin film becomes difficult to maintain and a liquid absorbed in the liquid absorbent layer easily oozes out to appear on the resin film and come into contact with the wearer's skin.
On the other hand, the liquid passage layer disclosed in Patent Publication No. H11-513904 is improved in resistance to liquid passage in the direction from the liquid absorbent layer to the skin-side surface of the liquid passage layer by stacking two resin films having a large number of liquid passage apertures. However, since the liquid passage apertures in the upper resin film have a large individual open area and the upper resin film has a large percent open area due to the liquid passage apertures, the upper resin film is apt to be compressed when subjected to body pressure. When the upper resin film, which comes into direct contact with the wearer's skin, is compressed, relatively stiff aperture edges around the liquid passage apertures tend to irritate the skin to cause pain or itching. At this time, moreover, since both the individual open area and the percent open area decrease in the upper resin film, the resistance to liquid passage is increased, so that an applied liquid such as menstrual blood is apt to remain on the skin-side surface of the liquid passage layer and adhere to the wearer's skin.